This is a continuation-in-part of U.S. Patent Application Ser. No. 709,903 filed on July 29, 1976, now abandoned, which, in turn, relates to an improvement of the container construction described in U.S. Pat. No. 4,151,927 filed on Feb. 6, 1976 and assigned to the same assignee as the instant case. In this respect, U.S. Pat. No. 4,151,927 is incorporated herein by reference.
Containers of the type described in U.S. Pat. No. 4,151,927 exhibited certain unexpected and outstanding strength characteristics when compared with similar characteristics of certain prior art types of cans. When the U.S. Pat. No. 4,151,927 types of cans were produced at top production-speeds, however, they sometimes had a tendency to increase the normally expected wear on the punches with which the cans were made. Illustrated embodiments of the instant invention, however, provide a container wherein such punch-wear is reduced.
Containers of the "drawn-and-ironed" type exhibit three main points of failure when subjected to compressive loads such as occur when the cans are filled and closed with a conventional end. Such failures tend to occur in either the can's neck portion or its sidewall or in the can's bottom. The instant invention provides a container wherein such failures occur most frequently in the container's bottom portion; and, moreover, can absorb relatively large quantities of energy before catastrophically failing in the sense that the container is no longer suited for its intended purpose. Moreover, as will be explained more fully shortly, cans of the invention are quite predictable in that failures can be expected to occur within a relatively narrow range of loads. Hence, they can be made from thinner stocks since smaller margins of error are permitted.
There are several advantages to providing a container that is most likely to fail at the bottom. In this regard, particularly in "drawn-and-ironed" containers, the thickness of the bottom does not differ significantly from the sheet stock with which such cans are normally constructed. Hence, the bottom-thickness of such cans can be relatively accurately controlled. It is the side-wall portions of these cans that are "drawn-and-ironed," however, and the side wall thicknesses, therefore, are more difficult to control. Consequently, to the extent a can's failure modes are primarily at the bottom, the can's strength can be more accurately controlled and its failures more accurately anticipated.
Additionally, the can of the instant invention is structured so that compressive forces cause initial deflection (a type of failure) in the bottom of the container; and, moreover, the bottom undergoes relatively large distortions before the can undergoes catastrophic failures such as in its side wall or neck. Consequently, so long as the compressive forces are not so large as to cause catastrophic failure, the container can still be filled and seamed without being discarded. In this connection, the can of the invention absorbs substantial quantities of energy as the bottom deflects. Consequently, it is possible to save more cans for filling and seaming than might otherwise be the case.
A still further advantage of the invention lies in the resulting can's ability to be constructed from a thinner gauge sheet stock. Similarly, as will become more apparent shortly, although more absorptive of energy, the can of the invention has a somewhat larger volume than that described in U.S. Pat. No. 4,151,927 and, to that extent, one embodiment of the invention has an even greater ability to have the position of its central portion selectively adjusted in order to maintain can-volume and accommodate relatively large amounts of tool-wear without requiring new tooling.
A further advantage of another embodiment of the invention is its tendency to have a center portion of its bottom "cricket" inwardly upon relief of pressure when the can is opened after filling. In this manner the particular embodiment is rendered more physically stable after it is opened even though its bottom has a tendency to "dome" outwardly when pressurized.